The dry developers used in electronic photography may be classified as one-part developers that use the toner itself, in which colorants have been dispersed among the terminal resin, and two-part developers wherein a carrier is mixed with the toner.
When copying using these developers, in order to establish a suitable process, the developer must have excellent fluidity, caking resistance, cohesiveness, electrostatic propensity, and cleaning. Inorganic fine particles have been added to the toner in order to increase said fluidity, caking resistance, cohesiveness, and cleaning.
In general, as shown in FIG. 1, external additives typically added to the toner surface have been inorganic particles such as silica (SiO2) and alumina (Al2O3), fluoride microparticles such as vinylidene fluoride and PTFE (polytetrafluoroethylene), and acryl and stylene-acryl resin microparticles manufactured by emulsion polymerization. In FIG. 1, the units are %.
The inorganic particles of the prior art, such as silica, have a diameter of 7-50 nm and are added in order to provide the toner with the fluidity of a powder. Ordinarily, when an external additive with a low particle radius is added to toner, the fluidity is good, but if the silica particle size is too small, it sometimes occurs that the silica separates from the toner surface due to stress applied to the toner, accordingly causing a gradual deterioration in fluidity over time; the size of the external additive particles has a powerful impact on print quality. In addition, because these inorganic particles exist on the far outside surface of the toner, they substantially impact the electrostatic propensity of the toner.
However, hydrophobized silica has strong negative electrostatic propensity, and hydrophobized alumina has strong positive electrostatic propensity, thus having a substantial electrostatic impact on the toner. Accordingly, there is an urgent need for a method of manufacturing monodisperse inorganic particles without aggregation among particles, with nanoscale particles that are also uniform in size and suitable for mass production, and that can be used in high-value-added high-definition toners and next-generation color toners that have a small particle size and require the addition of large quantities of external additives to the toner.